1. I have laboriously removed one bush leaving a huge gap- can another new one be planted in the gap? 2. Do I prune the existing bushes heavily to prevent the problem? (Now April) 3. Should I mulch and use native plant feriliser to prevent the problem? Can send photos by email but having difficulty attaching here. Many thanks as direct site visits presently difficult
Unfortunately, without a photo it will be hard to say. If the shrub died from disease, then it would not be a good idea to replant. If this died from something other than disease, then planting the same shrub back in the spot can be fine.
In the case of disease, it will be wise to treat the spot with fungicides. If the disease does not spread to the other shrubs, nearby, then it can be considered "controlled" and safe for planting.
Here is an article on fungicide use: